ADVERTISEMENT. THE handsome and flattering reception which the former volumes of this work has met with from the public, has afforded the author sufficient encouragement to proceed in the plan which he originally proposed. He trusts that his readers, and particularly those gentlemen and ladies who have introduced the Scientific Dialogues into their schools, will find that the subjects of Hydrostatics and Pneumatics are rendered, in most instances, perfectly familiar to the pupils who have attended to the Conversations on Mechanics to which he has occa❤ sionally referred. spe Perhaps in that part of the third volume which respects the specific gravities of bodies, the arithmetical operations, though rendered as familiar as the nature of the subject will admit of, may be deemed less easy than the other parts. To those young persons, however, who have studied the subject of decimals, which is by no means a difficult part of arithmetic, no obstacle will present itself, even in the method of obtaining, by experiment and calculation, the cific gravity of any body whetever. In some cases it may be desirable to pass over this part of the book till the reader be a little more grounded in arithmetical operations; but it would have been inexcusable in the author to have omitted it in his plan. The subject is important, and when understood, it will be found not less interesting than the other parts of the work. Authors in general have not illustrated this branch of Hydrostatics in a manner suited to the apprehension of young persons; and, on that account, it will be found discussed much at large in the Scientific Dialogues. It is hoped that the explanations of all the Hydrostatic and Pneumatic Engines are perfectly adapted to the understanding of those for whom this course of instruction is intended: that they are, in almost all cases, treated in a manner more familiar than has hitherto been attempted, will not, it is presumed, be denied. The author, in proof of this assertion, might, if he were inclined to mention particular instances, refer to the illustrations of the nature and principles of the Hydrostatic Paradox and of the echo and steam-engine; but he conceives he may confidently appeal to the judgment and decision of those that are accustomed to teach these branches of science, with respect to the whole of the volume now presented to the public. |